The proposed study aims to establish the relative contribution of central nervous system autonomic innervation of the heart to, and the effect of denervation on, the cardiovascular response to psychological stressors, and to examine the relationship of psychophysiological reactivity to the development of cardiovascular disease in heart transplant recipients. Twenty cardiac transplant recipients will be compared to matched heart surgery (innervated) control subjects and two groups of normal control subjects: 1) matched for age of the transplant patient and 2) matched for the age of the donor heart. Heart rate, systolic and diastolic blood pressure, cardiac output, and circulating epinephrine and norepinephrine responses to two standardized psychological stressors, mental arithmetic (MA) and a reaction time task (RT), will be evaluated. Cardiac output will be measured non-invasively by impedance cardiography. Power spectral analysis of heart rate variability will be used to determine the contribution of sympathetic and parasympathetic nervous system activity during psychological stress-testing. Subjects will be tested at three, six and twelve months after surgery (and at corresponding intervals for normal controls; normals matched for the age of the donor heart will be tested only at the three month interval) to test the hypotheses that: 1. a. Intact autonomic innervation is necessary for the full cardiovascular response to mental stress. b. Detectable reactivity will occur in denervated heart subjects, predominantly due to circulating catecholamines. Vagal effects will be absent. 2. Following denervation, the hemodynamic response to increases in catecholamines will change over time, reflecting adaptation. 3. High hemodynamic reactivity, within the cardiac transplant recipients, will be associated with increased subsequent cardiovascular disease (development of graft coronary artery disease).